Process for isomerization of liquid hydrocarbons



p 1957 N. c. CARTER EIAL 2,805,269

PROCESS FOR ISOMERIZATION OF LIQUID HYDROCARBONS Filed Ma 22. 1951 [0 AROMATIC AND/OR r12 EXTRACTION CYCLOPARAFFIN BLENDING FRACTION ALIPHATIC l4 FRACTION L ISOMERIZED ISOMERIZATION PARAFFINS l*- IN V EN TORS J. S. CROMEANS y N.C. CARTER A TTORNEVS United States Patent 6 PROCESS FOR ISOMERIZATION OF LIQUID HYDROCARBONS Norman C. Carter, Bartlesville, kla., and John S. Cromeans, Louisville, Ky., assignors to Phillips Petroleum Company, a corporation of Delaware Application May 22, 1951, Serial No. 227,632 22 Claims. (Cl. 260-6835) This invention relates to the production of high quality gasoline by a process of isomerization.

In one of its aspects the invention relates to a treatment of a liquid hydrocarbon fraction containing desirably isomerizable hydrocarbons and aromatics and/ or cycloparaflins prior to a catalytic isomerization of the said desirably isomerizable hydrocarbons. In another of its aspects the invention relates to the treatment of a gasoline to remove aromatics and/ or cycloparaflins therefrom prior to a catalytic isomerization of said gasoline employing a molybdenum oxide catalyst. In yet another aspect the invention provides a process for the preparation of an improved gasoline, e. g. higher anti-knock value, by removing from a gasoline any aromatic and/ or cycloparafiin compounds, isomerizing the remaining portion of the gasoline employing a supported, preferably prereduced, molybdenum oxide catalyst and then combining or blending the resulting isomerized portion with the said removed aromatic and/or cycloparafl'in com pounds.

It is known that liquid hydrocarbons consisting mainly of straight chain paraffin hydrocarbons of relatively low octane number may be substantially improved in octane numb-er by treatment with an isomerization catalyst whereby the straight chain hydrocarbons are converted into branched chain or isoparafiin hydrocarbons of high octane number.

I have found that liquid hydrocarbons containing substantial amounts of aromatics and/or cycloparaffins, on isomerization with a supported molybdenum oxide catalyst, yield poor results, due to low octane improvement and to poisoning of the catalyst by accumulation of cyclic hydrocarbons on the catalyst, relative to results obtained when the said aromatics and/or cycloparaflins are first removed.

The aromatics and cycloparafiin hydrocarbons generally have a high octane number in their original form and as a result when they are present in parafi'in hydrocarbons, the octane number of the mixture is higher than for naturally-occurring parafiin hydrocarbons alone. It has been found, according to this invention, that the aromatics and cycloparafiins are better used as blending agents than as feed stock to the isomerization process.

In accordance with the present invention, liquid hydrocarbons normally containing constituents which cause lowered effectiveness of the catalyst ar treated under extracting conditions with a solvent selective for the removal of the constituents which cause lowered effective ness of the catalyst. The refined hydrocarbon, mainly paraffins, after separation of the solvent and extract, is treated with the supported molybdenum oxide catalyst. The octane number of the treated parafiin hydrocarbon is substantially improved with increased effectiveness and yield per unit weight of catalyst. The aromatic and cycloparafiin hydrocarbons which are removed in the extract ca be recovered for use in blending with the isomerized paraflins or with other motor fuel. The liquid hydrocarbons to be isomerized by this process are most usually normal pentane, normal hexane and normal heptane but may include other liquid parafiin hydrocarbons such as normal octane, and longer chain parafiins.

Therefore, according to this invention, there is provided an improved process for the isomerization of gasoline components which comprises the steps of first removing any aromatics and/or cycloparafiins therefrom and then subjecting the remainder of the said gasoline to isomerization conditions in contact with a molybdenum oxide catalyst. As stated, the removed compounds or fraction can then be used to prepare an improved blend.

In case the proportion of aromatics and cycloparatfins in the hydrocarbon liquid is low, it may be desirable to treat the paraflinic hydrocarbons with sulfuric acid to. remove the small amount of aromatics and the cycloparaflins and then isomerize the treated paraffin, rather than to isomerize the hydrocarbon directly, or to solvent extract the feed and then isomerize.

Therefore, as a feature of this invention, and based upon its concepts, the gasoline can be first treated with an agent such as sulfuric acid forming desirable aromatic sulfonates which can be used as such or as intermediates or processed to recover the aromatics by known means.

It is believed now evident that the invention provides a flexible operation by means of which different charge stocks or gasoline can be most economically, yet effectively treated to obtain an improved gasoline and/ or sulfonates.

The preliminary solvent refining or extraction step may be carried out by conventional processes and with any solvent suitable for this purpose. The solvent extraction of light hydrocarbon oils is quite well known in the art, and it is intended that any of these methods may be used. Specific solvents which may be mentioned are sulfur dioxide, furfural, methyl alcohol, benzyl alcohol or mixtures of these. In carrying out the extraction process, the solvent is contacted with the hydrocarbon under temperature and pressure conditions to cause an extraction of aromatics and cycloparaifins, thereby forming an extract and raffinate layer, and then separating the two layers. Any solvent retained in the two layers may be removed, for example by distillation or washing with water. The raffinate layer will contain the paraffin hydrocarbons of low antiknock value. suitable for treatment by isomerization with supported molybdenum oxide catalyst. The extract layer after separation of the solvent will usually contain high antiknock hydrocarbons which may be used for motor fuel, for example, by reblending with the isomerized raflinate. The solvent will extract unsaturates along with the aromatics and cycloparafiins. These unsaturates also have a high octane number and may be used for blending with the isomerized raflinate.

For the isomerization catalyst, molybdenum oxide catalyst supported on alumina or on silica-alumina is preferred, although the molybdenum oxide may be supported 011 other materials known to the art. The catalyst may be prepared by impregnating the supporting material with an ammonium molybdate solution and subsequent calcining to form the supported molybdenum oxide catalyst. Preferably, the catalyst is prereduced although this is not essential to operativcness or good yields.

The isomerization of normal hexane with the supported molybdenum oxide catalyst is decreased by as much as 25 to 50 percent by the presence of cycloparafiins. This finding is wholly unexpected. Thus, cycloparafiins have no ill effect on aluminum chloride catalyst. The cycloparafiins are beneficial to the aluminum chloride catalyst, in fact, in that disproportionation is suppressed.

The deterioration of the molybdenum oxide catalyst activity may be retarded by carrying out the process in the presence of hydrogen. One function of the hydrogen appears to be that of minimizing deposition of carbon on the catalyst; The hydrogen-to-paraflin mol ratio should be larger than 0.03:1, preferably greater than 0.311 and less than :1. If the hydrogen in the feed is too low, the activity of the catalyst is so decreased by carbon deposition that the conversion per pass is disadvantageously low, and the selectivity of the catalyst, as indicated by the ultimate yield of isoparafin or branched paratlins is similarly adversely affected. Furthermore, when the hydrogen in the feed is too low, an appreciable proportion of olefins appear in the eflluent. The hydrogen may at least in part be recycled without purification and may contain an appreciable amount of gaseous by-products such as methane, etc. The probability that the hydrogen enters into the isomerization reaction should also be noted.

The reaction is effected, usually, under temperature and pressure conditions which maintain the vapor phase. The temperatures are preferably in the range of 815 to 860 5., although temperatures in the range of 780 to 885 F. may be used. Specifically, the preferred temperature range for the isomerization of normal pentane is 830 to 860 F. and for normal hexane the preferred temperature range is 815 to 830 F. The pressure may range from 100 to 950 p. s. i., however, a pressure of 250 to 550 p. s. i. is preferred. Specifically, the optimum pressure for isomerization of normal pentane is 250 to 500 p. s. i. and for normal hexane the preferred pressure range is 400 to 915 p. s. i. A contact time of 50 seconds to 350 seconds and preferably 100 to 150 seconds is used to obtain optimum conversion. Optimum conversion may be maintained with decreasing contact time by increasing the reaction temperature.

In order to describe the invention in more detail reference will now be made to the accompanying drawing. A liquid hydrocarbon, mainly parafiinic, and usually containing substantial amounts of cycloparatfins, aromatics and/ or unsaturates is conducted from a source not shown through pipe 10 to an extraction unit 11. A paraflin hydrocarbon fraction consisting mainly of pentane will contain no aromatics but can have a substantial amount of cycloparaffins. A hexane fraction can contain from 1 to 5 percent benzene and up to 20 percent cycloparaflins. In this extraction unit the liquid hydrocarbons are treated so as to extract from them cycloparafiin, aromatic and unsaturated hydrocarbons. This extraction may be effected'by treatment with a selective solvent such as sulfur dioxide. The cycloparaffin, aromatic and unsaturated hydrocarbons so extracted from the liquid hydrocarbons are separated from the extracting medium and passed to a tank 12 from which they may be passed, all or in part, to a tank 13.

After being freed from dissolved solvent by any suitable means, the liquid hydrocarbons from which the cycloparaflin, aromatic and unsaturated constituents have been removed are passed to a tank 14 and from there conducted to an isomerization unit 15 wherein they are subjected to contact along with added hydrogen with the isomerization catalyst molybdenum oxide-on-silicaalumina. The resulting branched chain parafiins are passed to a tank 16 from which they may be passed, all or in part, to the previously mentioned tank 13 for blending with the aromatic, unsaturated and cycloparafiin constituents previously referred to. Hydrogen and unreacted hydrocarbons may be recycled.

The process of the present invention, wherein the liquid hydrocarbon is treated to remove aromatics, unsaturates and cycloparaffins prior to isomerization, produces an ultimate yield of about 85 to 90 percent of product showing an octane improvement of about 25 to 70 points. Similar isomerization treatment without the preliminary solvent extraction treatment produces ultimate yields of only about 40 to 60 percent. Moreover, the catalyst is poisoned in a short time.

In plant practice, normal parafiin concentrate would usually be isomerized, such concentrate having a normal 4 l paraflin content greater than the equilibrium amount at the conditions of isomerization.

Example I A pure grade normal pentane of 99+ mol percent purity and having an ASTM octane number of 63, was admixed with hydrogen in a hydrogen-to-pentane mol ratio of 0.721, and the mixture was passed, in an isomerization step, through a solid fixed bed of molybdenum oxideonsilica-alumina. The catalyst was prepared by impregnat- Example II A pure grade hexane having an ASTM octane number of 26, was admixed with hydrogen in a hydrogen-tonexane mol ratio of 07:1, and the mixture was passed, in an isomerization step, through a solid fixed bed of molybdenum oxide-on-silica-alumina prepared as previously described. The isomerization was conducted at a temperature of 815 to 830 F., a pressure of 515 p. s. i., and a contact time of 105 to 112 seconds. An ultimate yield of branched hexanes of 85 percent with an ASTM octane number of about 81 was obtained at a total conversion of normal hexane per pass of 52.5 weight percent.

Example III A mixture of percent pure normal hexane and 20 percent methylcyclopentane was admixed with hydrogen, in a hydrogen-to-hydrocarbon mol ratio of 07:1 and the mixture was passed, in an isomerization step, through a solid fixed bed of molybdenum oxide-silica-alumina prepared as previously described. The isomerization conditions were the same as in Example 11. The total conversion of normal hexane per pass was 28.8 weight percent, a decrease of 45 percent by the presence of cycloparaffin. The catalyst was poisoned by the methylcyclopentane.

Example IV 96 percent pure normal hexane and 4 percent benzene was admixed with hydrogen, in a hydrogen-to-hydrocarbon mol ratio of 0.7:1 and the mixture was passed, in an isomerization step, through a solid fixed bed of molybdenum oxide-on-silica-alumina prepared as previously described. The isomen'zation conditions were the same as in Example II. The total conversion of normal hexane per pass was 37.0 weight percent, a decrease of 30 percent by the presence of aromatics. The benzene accumulated on the catalyst during the run.

It can readily be seen from Examples III and IV that it is highly desirable to remove the aromatic and/or the cycloparafiin before isomerization with M003, or a prereduced molybdena supported catalyst.

Variation and modification are possible within the scope of the foregoing disclosure and appended claims to the invention the essence of which is that an increase of both the yield and octane number can be obtained in the isomerization of a hydrocarbon fraction comprising aromatics and/ or cycloparaifins by the prior removal of any of said aromatics and/or cycloparaflins when the catalyst is a molybdenum oxide catalyst, preferably a supported molybdenum oxide catalyst, and still more preferably which catalyst has been prereduced and that a process has been set forth for the' said removal and the said subsequent isomerization of the remainder of the said hydrocarbon fraction, e. g. a gasoline.

We claim:

1. A. process for the preparation in. improvedv yield of a motor fuel having improved octane characteristics from an isomerizable hydrocarbon fraction containing. hydrocarbons suitable as components of a motor fuel and containing at least one of an aromatic hydrocarbon and a cycloparafiin hydrocarbon which comprises the steps of treating said hydrocarbon fraction to provide a portion: rich in said aromatic hydrocarbon and cycloparaflin hydrocarbon and a portion poor in said aromatic hydrocarbon and said cycloparafiin. hydrocarbon and isomerizing the said portion poor in said aromatic hydrocarbon and cycloparaflin hydrocarbon in presence of a molybdenum oxide catalyst supported upon a material selected from the groups consisting of alumina and silicaalumina, at a temperature in the range of 780 to 885 F., a pressure in the range 100 to 950. p. s. i. a. and a hydrogen to hydrocarbon mol ratio of 0.03:1 to :1.

2. The process of claim 1 wherein the temperature in the said isomerization zone is in the range 815 to 860 F., the pressure is in the range 250 to 550 pounds per square inch absolute, the hydrocarbons are. maintained substantially in the vapor phase the hydrogen to hydrocarbon mol ratio is greater than 03:1 and less. than 10:1, the time of contact is in the range of 50 seconds to 350 seconds and wherein the molybdenum oxide catalys is molybdenum oxide supported upon a carrier.

3. The preparation of an improved motor fuel in improved yield from a hydrocarbon fraction containing an isomerizable paraflin hydrocarbon, an aromatic hydrocarbon and a cycloparaflin hydrocarbon which comprises the steps of removing substantially all of said aromatic and said cycloparafiin hydrocarbon from said hydrocarbon fraction, and subjecting the remainder of said hydrocarbon fraction to isomerization conditions in the presence of a molybdenum oxide isomerization catalyst supported upon a material selected from the group consisting of alumina and silica-alumina and a hydrogen to hydrocarbon mol ratio of 0.3:1 to 10:1.

4. The preparation of an improved motor fuel in improved yield from a hydrocarbon fraction containing an isomerizable paraflin hydrocarbon and an aromatic hydrocarbon and a cycloparaflin hydrocarbon which comprises the steps of removing substantially all of said aromatic and said cycloparaflin hydrocarbon from said hydrocarbon fraction; subjecting the remainder of said hydrocarbon fraction to isomerization conditions in the presence of a molybdenum oxide catalyst and in the presence of hydrogen, the hydrogen to paraifin mol ratio being at least 0.03:1 and less than 10:1 and blending the isomerized hydrocarbon fraction with at least a portion of said removed aromatic and cycloparaffin hydrocarbon.

5. The preparation of an improved motor fuel component from a mixture containing a substantial proportion of normal hexane and a minor proportion of methylcyclopentane which comprises separating the methylcyclopentane from said mixture, admixing the normal hexane with hydrogen, and isomerizing said hexane hydrogen admixture in presence of a molybdenum oxide catalyst.

6. A process according to claim 5 wherein the isomerized admixture is treated to recover isomerized hydrocarbon and the said isomerized hydrocarbon is blended with the said methylcyclopentane.

7. The preparation of an improved motor fuel component from a mixture containing a substantial proportion of normal hexane and a minor proportion of benzene which comprises separating the benzene from said mixture, admixing the normal hexane with hydrogen, and isomerizing said hexane hydrogen admixture in presence of a molybdenum oxide catalyst supported upon a material selected from the group consisting of alumina and silica-alumina.

8. A process according to claim 7 wherein the isomerized admixture is treated to recover isomerized hydrocarbonand the said isomerized hydrocarbon is blended with the said benzene.

9.. The preparation of animproved motor fuel in improved. yield from a hydrocarbon fraction containing a paraflin hydrocarbon, an aromatic hydrocarbon and a cycloparaffin hydrocarbon which comprises the steps of removing substantially all of said aromatic and said cycloparaffin hydrocarbon from said hydrocarbon fraction; subjectingthe remainder of said hydrocarbon fraction to isomerization in the presence of a molybdenum oxide catalyst at a temperature in the range 780 to 885 F. and a pressure in the range to 950 p. s. i. a. and a hydrogen to hydrocarbon mol ratio of 0.3:1 to 10:1 and blending the isomerized hydrocarbon fraction with at least a portion of said removed aromatic and cycloparaflin hydrocarbon.

10. The preparation of an improved motor fuel in improved yield from a hydrocarbon fraction containing an n-paraflin hydrocarbon, an aromatic hydrocarbon and a cycloparaffin hydrocarbon which comprises the steps of removing substantially all of said aromatic and cycloparaflinhydrocarbons from said hydrocarbon fraction;v subjecting the remainder of said hydrocarbon fraction containing said n-paraflin hydrocarbon to isomerization in the presence of a molybdenum oxide catalyst supported upona material selected from the group consisting of aluminaand; silica-alumina at a temperature in the range 815 to 860 F. and a pressure in the range of 250 to 550 p. s. i. a. and a hydrogen to hydrocarbon mol ratio of 0.3:1 to 10:1; recovering a hydrocarbon fraction containing a substantially increased amount of isoparaflins; and blending the isoparafiin containing hydrocarbon fraction with at least a portion of said removed aromatic and cycloparafiin hydrocarbons.

11. The process of claim 10 wherein the normal paraffin hydrocarbon is normal pentane.

12. The process of claim 10 wherein said normal paraffin hydrocarbon is essentially normal hexane.

13. In the preparation of an improved motor fuel component from a mixture containing a major proportion of isomerizable parafi'in hydrocarbons and a minor portion of aromatic and cycloparaifin hydrocarbons which comprises contacting said mixture with sulfuric acid so as to sulfonate the aromatic and cycloparaflin hydrocarbons; separating the unreacted isomerizable paraflin hydrocarbons from said sulfuric acid containing sulfonates of said aromatic and cycloparaflin hydrocarbons; admixing the unreacted isomerizable paraflin hydrocarbons with hydrogen; and isomerizing said paraflin hydrocarbonhydrogen admixture in the presence of a molybdenum oxide catalyst supported upon a material selected from the group consisting of alumina and silica-alumina.

14. In the preparation an improved motor fuel component from a mixture containing isomerizable paraflin hydrocarbons and aromatic and cycloparafiin hydrocarbons the improvement which comprises the steps of contacting said hydrocarbon mixture with a solvent selected for the removal of the aromatic and cycloparafiin hydrocarbons under extracting conditions; separating the isomerizable parafiin hydrocarbons from said solvent and dissolved aromatic and cycloparafiin hydrocarbons; admixing said paraflin hydrocarbons with hydrogen; and isomerizing said parafiin hydrocarbon-hydrogen admixture in the presence of a supported molybdenum oxide catalyst supported upon a material selected from the group consisting of alumina and silica-alumina.

15. The process of claim 14 wherein said solvent is at least one selected from the group consisting of sulfur dioxide, furfural, methyl aclohol, and benzyl alcohol.

16. The process of claim 15 wherein said solvent is sulfur dioxide.

17. The process of claim 15 wherein said solvent is furfural.

18. The process of claim 15 wherein said solvent is methyl alcohol.

"7 19. The process of claim 15 wherein said solvent is benzyl alcohol. i

20. The preparation of an improved motor fuel in improved yield from a hydrocarbon fraction containing normal pentane, an aromatic hydrocarbon and a cycloparaflin hydrocarbon which comprises the steps of removing substantially all of said aromatic and said paraffin hydrocarbons from said hydrocarbon fraction, subjecting the remainder of said hydrocarbon fraction which is essentially normal pentane to isomerization at a temperature in the range of 830 to 860 F., a pressure in the range of 250 to 550 pounds per square inch and a hydrogen to hydrocarbon mol ratio of 0.3:1 to 10:1 in the presence of a molybedenum oxide isomerization catalyst supported upon a material selected from the group consisting of alumina and silica-alumina.

21. The preparation of an improved motor fuel in improved yield from a hydrocarbon fraction containing normal hexane, an aromatic hydrocarbon and a cycloparafiin hydrocarbon which comprises the steps of removing substantially all of said aromatic and said cycloparafiin hydrocarbons from said hydrocarbon fraction, and subjecting the remainder of said hydrocarbon which is essentially normal hexane to isomerization at a temperature in the range 815 to 830 F., a pressure in the range of 400 to 915 pounds per square inch and a hydrogen to hydrocarbon mol ratio of 0.321 to 10:1 in the presence of a molybdenum oxide isomerization catalyst supported upon amaterial selected from the group consisting of alumina and silica-alumina.

22QA process for the preparation in improved yield of a motor fuel having improved octane characteristics froman isomerizable hydrocarbon fraction containing hydrocarbons suitable as components of a motor fuel and containing at least one of an aromatic hydrocarbon and a cycloparaflin hydrocarbon which comprises the steps of treating said fraction to provide a portion rich in at least one of said aromatic and said cycloparaffin hydrocarbon and a portion poor in said last-mentioned hydrocarbons, admixing hydrogen with said portion poor in said lastmentioned hydrocarbons, and isomerizing said admixture in the presence of molybdenum oxide catalyst supported upon a material selected from the group consisting of alumina andsilica-alumina.

References Cited in the file of this patent UNITED STATES PATENTS 2,242,504 Benedict et al May 20, 1941 2,350,834 Sensel et 'al. June 6, 1944 2,424,636 Smith July 29, 1947 OTHER REFERENCES Turkevich et al.: Iour. Amer. Chem. 800., 519-520 (Feb. 1941) (2 pages). 

1. A PROCESS FOR THE PREPARATION IN IMPROVED YIELD OF A MOTOR FUEL HAVING IMPROVED OCTANE CHARCTERISTICS FROM AN ISOMERIZABLE HYDROCARBON FRACTION CONTAINING HYDROCARBONS SUITABLE AS COMPONENTS OF A MOTOR FUEL AND CONTAINING AT LEAST ONE OF AN AROMATIC HYDROCARBON AND A CYCLOPARAFFIN HYDROCARBON WHICH COMPRISES THE STEPS OF TREATING SAID HYDROCARBON FRACTION TO PROVIDE A PORTION RICH IN SAID AROMATIC HYDROCARBON AND CYCLOPARAFFINS HYDROCARBON AND A PORTION POOR IN SAID AROMATIC HYDROCARBON AND SAID CYCLOPARAFFINS HYDROCARBON AND ISOMERIZING THE SAID PORTION POOR IN SAID AROMATIC HYDROCARBON AND CYCLOPARAFFIN HYDROCARBON IN PRESENCE OF A MOLYBDENUM OXIDE CATALYST SUPPORTED UPON A MATERIAL SELECTED FROM THE GROUP CONSISTING OF ALUMINA AND SILICAALUMINA, AT A TEMPERATURE CONSISTING OF ALUMINA AND SILICAA PRESSURE IN THE RANGE 100 TO 950 P.S.I. A. AND A HYDROGEN TO HYDROCARBON MOL RATIO OF 0.03:1 TO 10:1. 